High frequency transfer of a broad host range plasmid present in an atypical strain of the fish pathogen Aeromonas salmonicida

Abstract

We have demonstrated transfer of a naturally occurring plasmid (pRAS1), encoding multiple resistance, from atypical Aeromonas salmonicida strain 718 to a variety of marine bacteria. This plasmid exhibited a broader host range and a generally higher transfer frequency when compared to the promiscuous plasmid RP4 originating from a hospital isolate of Pseudomonas aeruginosa. The plasmid pRAS1 was transferred from A. salmonicida to unrelated bacterial species and even to a Gram-positive bacterium (Lactobacillus sp.). Transfer of the plasmid was also shown to occur between A. salmonicida and 6 different bacterial isolates from fish farm sediments.